1. Field of the Invention
The present invention relates to a facsimile apparatus, and more particularly, to a facsimile apparatus comprising an image recovery circuit for recovering pseudo half-tone binary image data into image data of multi-gradation stages including an image density of half-tone (referred to as a multi-value image data hereinafter).
2. Description of the Related Art
In a conventional facsimile apparatus, for the purpose of transmitting an image signal through a public telephone line, a half-tone image such as a photograph image or the like is converted into pseudo half-tone binary image data by binarizing the half-tone multi-value image data by a dither method or the like at the transmitting terminal, while at the receiving terminal the received pseudo half-tone binary image data are recovered into multi-value image data.
A method and an apparatus of this type are disclosed, respectively, in Japanese Patent Application Laid-Open Publications Nos. 62-114378 and 62-107573.
The former first conventional image processing method has such a feature that a multi-value printer is used even for processing conventional type binary image data to sufficiently draw the capability of the apparatus, and to improve the quality of character images to be recovered, a half-tone image is recovered from the binary image data and then the recorded binary image data are subject to a prescribed image process such as an image expansion process, an image reduction process, an image emphasis process or the like. According to the first conventional method, in order to convert the binary image data into the multi-value image data by a recovering process, a square window having specified dimensions has been set up around a pixel to be recovered or processed (referred to as "a specified pixel" hereinafter) to perform a smoothing process within the square window.
Further, the latter second conventional image processing apparatus has the following features. In order to prevent possible image deterioration from occurring when a simple binary circuit for effecting the process using the dither method or the like and also to allow the apparatus to be made up of simple circuits, the second image processing apparatus is provided with means for dividing binary image data into prescribed block areas, discrimination means for discriminating a kind of image tone of each of the divided block areas, and conversion means for converting the image data of each of the block areas into image data having multi-value levels every pixel according to the discrimination result of the discrimination means. In the above-mentioned second image processing apparatus, binary image data are handled upon transmitting and storing image data to increase the efficiency in editing the image of the image data displayed on a display, while the image is expressed in a form of multi-value image similar to an analog image upon reproducing the image. The above-mentioned discrimination means and the conversion means are in practical composed of an image tone judgment ROM for judging image tone using a pattern matching method within a block area corresponding to a dither matrix size and a conversion ROM, respectively.
By performing the above-mentioned recovery of binary image data into multi-value image data, the received image can be printed out as a multi-value image. However, since the image data are once converted into binary image data in the course of data transmission, the resulting image cannot be prevented from deteriorating in fidelity and resolution with respect to the original.
In the above regard, any conventional facsimile apparatus transmits a non-half-tone image such as a character image in the form of binary image data, and further transmits a half-tone image such as a photograph image in the form of pseudo half-tone binary image data. Therefore, the conventional facsimile apparatus does not transmit multi-value image data, which means that there has been no facsimile apparatus capable of managing multi-value image data as received image data.
In view of the above, it can be considered to transmit image data in the form of compressed multi-value image data, and data compression and expansion method (referred to as "a third conventional method" hereinafter) for transmitting multi-value image data of a color still image through a communication line is disclosed, for example, in Saito, et al. "Lecture on Image Data Compression of Still Image Coding System", Television Academy Journal, Vol. 44, No. 2, February, 1990 According to the above-mentioned third conventional method, a data compression and expansion process is performed by the ADCT (Adaptive Discrete Cosine Transform) coding method.
Therefore, it is expected that the above-mentioned type of facsimile apparatus for transmitting image data in the form of multi-value image data will be popularized in future. However, since facsimile apparatuses which transmit image data in the form of binary image data are widely used currently, such a future facsimile is also required to cope with binary image data transmitted from the current facsimiles to avoid practical inconvenience.